The present invention relates generally to catalysts and methods for converting light hydrocarbons into monohaloalkanes and other useful products. In particular, the invention is directed to the production of monochloromethane and formic acid from methane. As has been described in the inventors' prior U.S. Pat. No. 4,769,504, entitled "Process for Converting Light Alkanes to Higher Hydrocarbons", issued Sept. 6, 1988, monochloromethane so produced can be further processed to form gasoline boiling range hydrocarbons. This prior U.S. patent is hereby incorporated by reference for describing this process.
The need to supplement petroleum supplies has stimulated research and the production of chemicals and fuels from other sources. Methane from natural gas and from the conversion of coal is a source of considerable interest for such production.
It is well known that methane can be converted to methanol by reformation with steam and that the methanol thus produced can be further processed over a crystalline aluminosilicate catalyst to form gasoline boiling range hydrocarbons. Such a process is described in U.S. Pat. No. 3,928,483 to Chang et al.
Monohalomethanes can be prepared as disclosed in European Patent Application No. 0117731 and as suggested in PCT Publication No. W085102608, converted to higher hydrocarbons over crystalline aluminosilicates. It has long been thought that the monohalides are much preferred in such processes with only low levels of polyhalogenated alkanes tolerated for effective conversion. Such monohalomethanes can be produced by reaction of chlorine or other halogens with methane which requires elevated temperatures above 450.degree. C. or by the oxyhalogenation of methane using a suitable catalyst such as the halide salts of copper, nickel, iron or palladium. Such procedures as are described in the above cited European Patent Application are characterized by low conversions, generally less than about 35%.
An oxyhydrochlorination catalyst containing copper chloride, potassium chloride and a rare earth chloride is disclosed in U.S. Pat. No. 4,123,389 to Pieters et al. This catalyst is reported to provide substantially higher values of methane conversion, but to result in substantial polychlorination. Previously, this catalyst was of particular interest in the production of carbon tetrachloride as a feed stock for chlorofluorocarbon-refrigerants.
This invention also relates to the production of formic acid as a co-product to monohalide alkanes. Typically, formic acid is produced by the reaction of sulfuric acid with sodium formate in the presence of 85-90% formic acid. Adequate cooling of the reaction mixture and the presence of the added formic acid as a reaction medium limits decomposition of the product. Sodium formate is formed by the reaction of sodium hydroxide and carbon monoxide, such as from producer gas that is carefully cleaned and compressed to 12-18 atmospheres. The sodium formate crystals are obtained by drying the reaction product prior to reaction with the sulfuric acid.
The major commercial use of formic acid is in the textile and leather industries as an effective disinfectant and preservative. It acts as a dye exhausting agent for various fabrics and for other functions in dying and treating textiles. Formic acid serves as an intermediate in the preparation of various esters and amides. Methyl and ethyl formate have value as solvents, fumigants and pesticides. Formamide is of particular interest as it has considerable value in the manufacture of pharmaceuticals, agricultural chemicals and dyes.